Pre/Power Amplifiers

D'Agostino's inaugural Momentum power amp [HFN Jul '11] has evolved through the M400 [HFN Oct '16] to the M400MxV we have here, the latter two models rated at 400W/8ohm and both exceeding this by some margin at 430W/8ohm and 810W/4ohm (M400) and 435W/8ohm and 840W/4ohm (M400MxV). Their respective dynamic outputs are very similar too at 475W, 940W, 1775W and 3010W (M400) versus 440W, 845W, 1650W and 3050W (M400MxV) into 8, 4, 2 and 1ohm loads, respectively [Graph 1, below]. The 1ohm figure promises a very substantial 55A/10msec current capability at <1% THD indicating what we already know – the M400MxV will drive any loudspeaker that's likely to cross its path even if, in practice, it's no more powerful or load tolerant than its predecessor.

The real story behind the M400MxV has less to do with raw power than D'Agostino's 'tuning' of the amplifier's input and output stage configurations. This version, quite frankly, is simply more 'colourful' and also subjectively more 'relaxed' if the figures are any guide. Specifically, reduced feedback means distortion is higher than the M400's 0.04-0.17% (20Hz-20kHz/10W) but very consistent at ~0.05-0.06% through bass and low midrange over its 400W bandwidth, increasing at HF from 0.25%/1W to 0.75%/10W and 2.2%/100W [all 20kHz/8ohm, see Graph 2]. The output impedance is also slightly higher too, from ~0.15ohm (M400) to ~0.18ohm here just as the response is 'sweetened' from –0.12dB/20kHz and –2.0dB (M400) to –1.1dB/20kHz and –9.7dB/100kHz in the M400MxV. Subsonic bass remains flat to 1Hz but noise – an innocuous white noise – is higher, leading to a reduced 84.0dB A-wtd S/N ratio (re. 0dBW). PM